This invention relates to a flexible disk drive for rotatably driving a flexible disk inserted or loaded therein by a direct-drive (DD) motor such as a spindle motor.
In the manner which is well known in the art, the flexible disk drive (which may be hereinafter called “FDD” for short) of the type is a device for carrying out data recording and reproducing operation to and from a disk-shaped magnetic recording medium of the flexible disk (which may be hereinafter called “FD” for short) loaded therein. In addition, such a flexible disk drive is mounted or loaded in a portable electronic equipment such as a laptop personal computer, a notebook-size personal computer, a notebook-size word processor, or the like.
The flexible disk drive of the type comprises a magnetic head for reading/writing data from/to the magnetic recording medium of the flexible disk, a carriage assembly for supporting the magnetic head at a tip thereof with the magnetic head movably along a predetermined radial direction to the flexible disk, a stepping motor for moving the carriage assembly along the predetermined radial direction, and a spindle motor for rotatably driving the magnetic recording medium with the floppy disk held. The spindle motor is one of direct-drive (DD) motors.
In order to control such a flexible disk drive, an FDD control apparatus is already proposed. By way of example, Japanese Unexamined Patent Publication Tokkai No. Hei 9-97,493 or JP-A 9-97493 discloses, as the FDD control apparatus, one integrated circuit (IC) chip which incorporates first through third control circuits therein. The first control circuit is a reading/writing (hereinafter called “R/W”) control circuit for controlling reading/writing of data. The second control circuit is a stepping motor (hereinafter called “STP”) control circuit for controlling drive of the stepping motor. The third control circuit is a general controlling (hereinafter called “CTL”) control circuit for controlling whole operation of the flexible disk drive. The CTL control circuit may be called a logic circuit. This IC chip is generally implemented by a metal oxide semiconductor (MOS) IC chip where a number of MOS field effect transistors (FETs) are integrated therein.
The FDD control apparatus comprises not only the one IC chip but also a spindle motor IC chip for controlling drive of the spindle motor. The spindle motor IC chip is implemented by a bipolar IC chip where a number of bipolar transistors are integrated therein.
Now, flexible disk drives have different specifications due to customers or users. The specification defines, for example, drive select 0 or 1, the presence or absence of a special seek function, the presence or absence of an automatic chucking function, a difference of logic for a density out signal, a difference of logic for a mode select signal, 1 M mode 250 kbps or 300 kbps, and so on. If development is made of one IC chips which individually satisfy the different specification, a number types of one IC chips must be prepared. In order to avoid this, a one IC chip having a selectable function circuit is already proposed, for example, in Japanese Unexamined Patent Publication Tokkai No. Hei 9-97,839 or JP-A 9-97839 wherein all functions satisfying all specifications are preliminarily incorporated therein and one of the functions is selected in accordance with a particular specification.
In the manner which is well known in the art, the flexible disk driven by the flexible disk drive includes a disk-shaped magnetic recording medium accessed by the magnetic head. The magnetic recording medium has a plurality of tracks on a surface thereof that serve as paths for recording data and that are formed in a concentric circle along a radial direction. The flexible disk has eighty tracks on one side which include the most outer circumference track (which is named “TR00”) and the most inner circumference track (which is named “TR79”). The most outer circumference track TR00 is herein called the most end track.
It is necessary to position the magnetic head at a desired track position in a case where the flexible disk is accessed by the magnetic head in the flexible disk drive. For this purpose, the carriage assembly for supporting the magnetic head at the tip thereof must be positioned. Inasmuch as the stepping motor is used as a driving arrangement for driving the carriage assembly, it is possible for the flexible disk drive to easily carry out the positioning of the carriage assembly. In spite of this, it is necessary for the flexible disk drive to detect only the position of the most end track TR00 in the magnetic recording medium of the flexible disk loaded therein. In order to detect the position of the most end track TR00, the carriage assembly is provided with an interception plate which projects from a base section thereof downwards and a photointerrupter is mounted on a substrate in the vicinity of a main frame opposed to the carriage assembly. For example, see Japanese Unexamined Patent Publication Tokkai No. Hei 9-91,859 or JP-A 9-91859. That is, it is possible to detect that the magnetic head is laid in the position of the most end track TR00 in the magnetic recording medium of the flexible disk because the interception plate intercepts an optical path in the photointerrupter. Such a track position detecting mechanism is called a “00 sensor” in the art.
In the flexible disk drive where the DD (direct-drive) motor such as a spindle motor is used for rotatably driving the flexible disk, an index signal is generated on the basis of operation in periphery of a rotor of the DD motor. More specifically, a notch portion is partially provided with a peripheral side surface of a disk-shaped casing composing the rotor while a magnet is disposed inside the casing so that only one magnetic pole (e.g. a north pole) is visible via the notch portion. Such a magnet is called an index detection magnet. In addition, on a main frame on which a stator of the DD motor and so on are mounted, a main printed wiring board on which a predetermined circuit is formed is disposed. A Hall element is located on the main printed wiring board at a predetermined position corresponding to the outside of the rotor. The Hall element is called an index detection Hall element.
Herein, the Hall element is a semiconductor element applying a Hall effect. The Hall element is a phenomenon where an electric field occurs in a conductor in a y-direction perpendicular to both of an x-direction and a z-direction when the electric current flows in the x-direction in the conductor and when the magnetic field is applied in the z-direction perpendicular to the x-direction. The electric field caused thereby is a Hall electric field and an output of the Hall element in response thereto is a Hall output.
In addition, Hall elements are used not only as the index detection Hall element but also for detecting a position in the rotor of the spindle motor. Such Hall elements are called position detection Hall elements. A spindle motor using the position detection Hall elements is called a Hall motor.
Although the Hall motor requires three position detection Hall elements, in order to omit their position detection Hall elements, proposal is made to a new motor where states of currents flowing in three-phase coils of the stator are switched on the basis of polarity of an electromotive force induced in one of the three-phase coils that is put into a high-impedance state (e.g. see Japanese Unexamined Patent Publication Tokkai No. 2000-245,125 or JP-A 2000-245125).
In the manner which is described above, in prior art, a single-pole magnetized magnet is used as the index detection magnet. It is difficult to obtain a stable generation timing for the index signal. Accordingly, in order to obtain the stable generation timing for the index signal, the present co-inventors already proposes and files an application to use, as the index detection magnet, a double-pole magnetized magnet (that is, one where a south pole and a north pole are put side by side) (see Japanese Unexamined Patent Publication Tokkai No. 2001-190,055 or JP-A 2001-190055).
In addition, the index detection magnet mounted on the rotor and the index detection Hall element located on the printed wiring board are disposed so that they are apart from each other at a magnetic field detection position by a little distance. The printed wiring board is disposed so as to extend in a direction normal to a rotation axis of the spindle motor. Accordingly, a conventional index detection Hall element necessarily has a magnetic detection surface which is disposed to extend in parallel with a direction of the magnetic field generated by the index detection magnet.
In the manner which will later be described in conjunction with FIGS. 1 through 9, the conventional flexible disk drive must comprise not only a main frame but also a motor frame for mounting the DD motor (spindle motor) thereon. In other words, the motor frame is constituted as another piece different from the main frame.
In the conventional DD motor (the spindle motor), a permanent magnet composing a rotor has a bottom portion opposite to a main surface of the motor frame (a main surface of the printed wiring board) that is subjected to motor-servo magnetized elements along a circumferential direction thereof. The main surface of the motor frame and the bottom portion of the permanent magnet are opposite to each other with a predetermined gap so as to enable to detect the motor-servo magnetized elements by a frequency generation pattern.
In the DD motor (the spindle motor), on rotating the rotor, an adsorption force (a magnetic attractive force) between the permanent magnet composing the rotor and the motor frame acts as a torque loss against a rotation direction of the DD motor. In order to improve a motor torque of the DD motor (the spindle motor), it is desirable to weaken the adsorption force for the motor frame by the permanent magnet by widening the above-mentioned gap as far as possible.
However, in the conventional DD motor (spindle motor), the bottom portion of the permanent magnet opposite to the motor frame is subjected to the motor-servo magnetized elements along the circumferential direction thereof. Therefore, if the above-mentioned gap is widened, the frequency generation pattern produces the counterelectromotive force having a small output caused by rotation of the rotor (the motor-servo magnetizes elements of the permanent magnet). Accordingly, in the conventional flexible disk drive, it is difficult to widen the above-mentioned gap in the DD motor (the spindle motor) up to a predetermined distance or more. As a result, it is difficult to prevent the torque loss in the DD motor (the spindle motor).